AMINE EXTRACTION OF HYDROXYCARBOXYLIC ACIDS .2. COMPARISON OF EQUILIBRIA FOR LACTIC, MALIC, AND CITRIC ACIDS

Lactic, malic, and citric acids are representatives of hydroxycarboxylic acids, and they are also important biotechnological products. Extraction equilibria of these acids in the system water-solution of trialkylamine in mixtures of 1-octanol/ n- heptane at temperatures 25, 50, and 75-degrees-C have been measured. Mathematical models of diverse complexity are presented, and their goodness of fit is tested and mutually compared. The best, fits display the models comprising the formation of three acid-amine complexes and the nonideality of organic phase. In the cases of lactic and malic acids the acid -amine complexes (l,l), (2,1), and (2,2) and in the case of citric acid the complexes (1,1), (1,2), and (2,3) have been included. The incorporation of dissociation in the aqueous phase and of its nonideality has been found to have little effect on the model accuracy. The effects of temperature and solvent composition on the extraction equilibria have been studied, and exponential relations for their prediction have been derived. All the three systems display sensitivity to both temperature and solvent composition. Accordingly the principles of 'temperature and diluent swings' are applicable to the processes of extractive recovery and purification of the acids investigated.